The overall objective of this project is to develop highly stable electrochemical probes for the monitoring of the reduced cofactor nicotinamide adenine dinucleotide (NADH), which is produced in many enzyme-based immunoassays. These sensors can measure NADH concentrations at low applied potentials, where electrochemical interferences and deactivating chemical reactions are avoided. The Phase I research will attempt to establish the feasibility of using these new sensors for the measurement of NADH produced in clinically important immunoassays. The development of an electrochemical probe which can selectively measure NADH concentrations could permit analysis of very small samples, which is of importance, for example, to clinical assays of neonatal blood samples. During the Phase II program, the construction and testing of small sample chambers (e.g., "capillary" immunoassays), for use with these electrochemical sensors, could lead to the development of rapid, automated immunoassays requiring very small amounts of sample.